The cellulose acylate film is widely used as a phase difference film for a liquid crystal display due to its transparency, toughness, and optical isotropy.
Production of the cellulose acylate film is broadly divided into a solution film-forming method and a melt film-forming method. The solution film-forming method is a method where a dope obtained by dissolving a thermoplastic resin in a solvent is cast into a film from a die on a support, for example, a cooling drum. The melt film-forming method is a method where a thermoplastic resin is melted in an extruder and, thereafter, is extruded into a film from a die on a support, for example, a cooling drum. An unstretched cellulose acylate film formed by these methods is usually stretched in the machine (longitudinal) direction or transverse (width) direction (to obtain a stretched cellulose acylate film) for the film to develop an in-plane retardation (Re) and a thickness direction retardation (Rth). This film is used as a phase difference film for a liquid crystal display to widen the viewing angle (see, for example, Patent Document 1 and Patent Document 2).    Patent Document 1: National Publication of International Patent Application No. H6-501040    Patent Document 2: Japanese Patent Application Laid-Open No. 2001-42130